The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
Screening of samples using transmission electron microscopy (EM) is often used in to characterize proteins such as antibodies used for therapeutics, viruses or virus like particles used in vaccines, drug delivery particles, or other formulations of nanoparticles. Screening may also be used to determine optimal conditions for 2D and 3D crystallization of proteins, optimizing preparation conditions for a novel protein or other macromolecular complexes, as well as formulation optimization.
EM applications such as those discussed above often require the analysis of a large number of conditions in parallel. EM sample preparation typically requires a cumbersome procedure of obtaining several negative stained samples on EM grid supports for each condition. EM grids typically comprise of a 3 mm diameter copper mesh (˜25 μm thick) with open square windows (30 to 200 μm wide) acting as the base substrate. A thin (typically 5-50 nm) carbon film is layered on top this substrate, creating electron transparent (carbon film) regions in the open windows. Other EM grid substrate materials are usually made of other metals or semiconductor materials such as silicon, with films made of Silicon Nitride, Silicon Dioxide or Silicon Carbide. By way of example, each condition being analyzed can require (i) plasma treating one or more grids to create a hydrophilic specimen surface, (ii) pipetting 2-3 μL of the appropriate sample in an appropriate buffer onto the specimen surface, (iii) blotting the grid using filter paper to remove excess sample, (iv) pipetting 2-3 μL of stain immediately onto the specimen surface to avoid sample drying, (v) blotting the grid again using filter paper to remove excess stain, and (vi) allowing the stain to dry. In many cases staining using this process requires optimization of several conditions, such as concentration (sample and stain), buffer constituents, pH, sample and stain application time. This results in a large number of grid trials, which entail loading individual grids into the electron microscope for analysis of each condition, and wastes large volumes of what are often very precious sample material.